1. Field of the Invention
The present invention relates to a process for manufacturing a board used as a core in decorative laminates and a decorative laminate obtained by the process.
2. Description of the Related Art
Products clad with thermosetting laminates are quite common nowadays. They are most often used where the demand for abrasion resistance is great but also where resistance towards different chemical substances and moisture is required. Floors, floor skirtings, work tops, table tops, doors and wall panels can serve as an example of such products. The thermosetting laminate is most often made from a number of base sheets and a decorative sheet placed closest to the surface. The decorative sheet may be provided with the desired decor or pattern. Thicker laminates are often provided with a core of particle board or fibre board where both sides are covered with sheets of thermosetting laminate. The outermost sheet is, on at least one side, most often a decorative sheet. One problem with such thicker laminates is that the core is much softer than the surface layer which is made from paper impregnated with thermosetting resin. This will cause a considerably reduced resistance towards thrusts and blows compared to a laminate with a corresponding thickness made of paper impregnated with thermosetting resin only.
Another problem with thicker laminates with a core of particle board or fibre board is that these normally will absorb a large amount of moisture, which will cause them to expand and soften whereby the laminate will warp. The surface layer might even, partly or completely come off in extreme cases since the core will expand more than the surface layer. This type of laminate can therefore not be used in humid areas, such as bath rooms or kitchens, without problem.
The problems can be partly solved by making the core of paper impregnated with thermosetting resin as well. Such a laminate is most often called compact laminate. These compact laminates are, however, very expensive and laborious to obtain as several tens of layers of paper have to be impregnated, dried and put in layers. The direction of the fibre in the paper does furthermore cause a moisture and temperature difference relating expansion. This expansion is two to three times as high in the direction crossing the fibre than along the fibre. The longitudinal direction of the fibre is coinciding with the longitudinal direction of the paper. One will furthermore be restricted to use cellulose as a base in the manufacturing though other materials could prove suitable.
It is known to manufacture boards of recycled rigid polyurethane foam particles bonded by using MDI as a glue. These polyurethane particle boards are, however, not suited as cores in laminates such as the ones described above since the particles normally will expand when heated. This expansion will cause blistering close to the surface which will cause the surface to de-laminate locally from the core. Another problem with such polyurethane based boards is that they absorb moisture up to a level of about 5% calculated on a 100% relative humidity environment. Humidity absorption will cause expansion which leads to de-lamination and possibly warping of such boards.
The above problems have through the present invention been solved whereby a flexible process for the manufacturing of a mainly isometric and preconditioned core to a decorative laminate has been achieved. Accordingly the invention relates to a process for the manufacturing of a core forming a carrying structure for decorative laminates. The core comprises particles of cured, and possibly foamed, rigid, polyurethane, polyisocyanurate and/or phenolic resin, which particles are bonded to each other in a pressing procedure with a bonding agent comprising an adhesive such as a polymerizing monomer. The invention is characterized in that;
i) The particles are achieved by grinding cured, and possibly foamed, rigid, polyurethane, polyisocyanurate and/or phenolic resin so that it passes through a 2 mm screen, preferably a 1 mm screen;
ii) The particles are allowed to absorb a selected amount of water, the amount of water being in the range 1-15% by weight. The water is either added at any stage before the adding of bonding agent, and/or being used as a solvent in the bonding agent;
iii) 85 parts per weight of the particle mixture is mixed with 2-15 parts per weight of a bonding agent, the bonding agent selected from the group consisting of,
a) a mixture of polyols, such as polyester or polyether, crude methylene diphenyl diisocyanate and possibly a small amount of blowing agent in a ratio forming a polymeric resin with a density in the range 600-1400 kg/m3;
b) the bonding agent may also or alternatively consist of a formaldehyde based resin such as phenol-formaldehyde resin, urea-formaldehyde resin, melamine-urea-formaldehyde resin, melamine-urea-phenol-formaldehyde resin or phenol-resorcinol-formaldehyde resin;
c) the bonding agent may also or alternatively consist of polyvinyl acetate resin;
iv) the mixture is applied in a continuous or static press, possibly with at least one intermediate carrier web, the press allowing a mainly uniform and specified material thickness to form, whereby a slightly porous and preconditioned core with a selected water content in the range 0.8-12% by weight is achieved.
The pressure cycle characteristics are typically in the range; pressure 20-70 MPa, temperature 110xc2x0 C.-170xc2x0 C. and a duration of 45 seconds-4 minutes. It is possible to achieve boards with different mechanical properties by altering the pressure cycle characteristics as well as the raw material composition within the scope of the invention. However typical process parameters would suitably be: pressure 50 MPa, temperature 150xc2x0 C. and a duration of 3 minutes.
A flame retardant comprising halogens such as tri-chlorophosphate is preferably included in the mixture forming the core.